1. Field of the Invention
The present invention relates to a GE-PON (Gigabit Ethernet—Passive Optical Network) system, and more particularly to a redundant apparatus and method for switching a path between an OLT (Optical Line Terminal) and a splitter, and a frame format thereof
2. Description of the Related Art
Typically, a PON system has a Point-To-Multipoint structure where one central node (i.e., one OLT) is connected to a plurality of regional nodes (i.e., a plurality of optical network units (ONUs)) by means of a passive optical splitter on an optical cable.
FIG. 1 is a block diagram illustrating an overall configuration of a conventional GEP-PON system. A 1×N passive optical splitter connects one OLT to a N ONUs in a tree-structured distribution topology.
FIG. 2 illustrates a format of a legacy OAM (Operation, Administration and Maintenance) frame. “DA” is a destination address and “SA” is a source address. The remaining fields are reference characters. In particular, “SUBTYPE” contains a prescribed value of 0×03 (i.e., the hexadecimal digits “0” and “3”). “VER” indicates version information, “FLAG” indicates flag information, and “OPCODE” indicates an operation code. “FCS” is an abbreviation of a Frame Check Sum. The field lengths, in octets (8 bits), for the nine fields shown in FIG. 2 are six, six, two, one, one, one, one, 106 and four, respectively.
An automatic switching system prescribed in an ITU-T G.783 performs a switching function using K1 and K2 bytes of a SDH (Synchronous Digital Hierarchy).
Presently, ITU-T G.983.5 completes a standardization of an enhanced survivability, broadband optical network and uses an additional standardization frame. However, the additional frame such as a PLOAM (Physical Layer Operation, Administration and Maintenance) having respective individual fields of K1 and K2 bytes to enhance survivability of the broadband optical network is implemented with a difference between an upstream format and a downstream format.
The ITU-T G.983.5, moreover, is directed to an ATM-PON (Asynchronous Transfer Mode—Passive Optical Network) topology and frame format, whose frame transmission method and characteristics are incompatible with the emerging IEEE 802.3ah “Ethernet in the First Mile” (EFM) OAM switching scheme.
There are three kinds of switching methods between an OLT and a splitter, that is, an OLT-only protected system, a fully protect system for switching an overall area ranging from the OLT to an ONU, and an X:N switching system. However, an OAM track based on the IEEE 802.3ah EFM being currently standardized does not describe an improved scheme for implementing functions associated with a switching request.